__________________1st rule of yachting: When a collision is unavoidable, aim for something cheap.
"whatever spare parts you bring, you'll never need"--goboatingnow
"Id rather drown than have computers take over my life."--d design

Another update here. I got one side done relatively easy. Used a router to cut away some of the balsa core and replaced the core with west systems six10 thickened epoxy. I bolted the chain plate in place, only covered with grease so that the epoxy could form a "perfect fit" around the chain plate. Here's how it came out:

This is what the core looked like on the opposite side of the deck after I eventually took a screw gun, with an allen key and a vacuum cleaner and went to town clearing out the 3" of core surrounding the chain plate. Now that it is cleared out, just refill with epoxy, right? WRONG!

As soon as I got the caulk gun loaded and squirted the first little bit of epoxy into on of the holes, the caulk gun broke
So I run to home depot with the epoxy in the fridge, trying to slow the curing process down.
I get back and it starts pouring down rain. For hours

Now here we are two days later. I am heading over after work in hopes that the holes has dried enough for the epoxy to at least stick to the hollow glass near the chain plate.
That good deal I got on this boat isn't sounding so good now lol

I did the same to a C&C I used to own, the core rot wasn't as extensive as yours, just about an inch around the chainplate slot, but still enough to cause concern. One trick I've used on that one and several others with moisture in the core was to cover the hole inside the boat and pour isopropal alcohol into the effected area, let it sit for awhile and then open up the hole for ventilation. Put a mild heat lamp or even just a clip lamp pointed at the underside of the deck to warm it and aid evaporation.
The alcohol is hydroscopic, it combines with the moisture in the core and then evaporates more easily, it has helped speed up the drying process.
Nice job by the way.

__________________1st rule of yachting: When a collision is unavoidable, aim for something cheap.
"whatever spare parts you bring, you'll never need"--goboatingnow
"Id rather drown than have computers take over my life."--d design

Thanks it was a somewhat frustrating process, but in the end I am very pleased with the results and being that it was all DIY. I know it was done right because I did it.

I want to share the method I used for the side I had to remove 3" of core from:

The six10 epoxy is an awesome product(especially for noobs like me), I can't believe they didn't think of it sooner...however, the consistency seemed a little thick to fully fill the 3" gap by just squirting it into the chain plate slot, so I borrowing a trick from the notorious "drill-n-fill" technique.

Once It was hollowed out, I drilled holes along the outer perimeter of the area of deck that I hollowed out.(I used the allen key that was inserted into the drill to measure with)
After the holes were drilled, I vacuumed out the dust rinsed with alcohol and let it sit in the hot sun for 24 hours.
At that point I greased up the chain plate and bolted it into place. After that, I loaded up a caulk gun with the six10 epoxy, then, working from the lowest point, I injected it into all the holes, until epoxy oozed out of the slot the the chain plate sits in. Once I got to the top I cleaned everything up and let it sit for 24 hours.
The next day I pulled the chain plate out, cleaned the grease off, bolted it back in place, cleaned with alcohol, then I sealed it with 3m 4000UV.
I attached a pic of what it looks like now. I plan on painting over the holes as soon as it stops raining.
BTW I used the polishing wheel to polish those little plates that screw on and hold the sealant in. I also passivated them as well...just because I can lol.
Looks like I've already found another use for the polishing wheel I didn't want to buy. Win-win!